The Experimental Research Of The Lung Injury Caused By Mechanical Ventilation And Oxygen Inhalation In The New-born Rabbit

Objectives: To investigate the tissue pathological change and the change of matrix metalloproteinase[MMPs]-2, 9 expression and the changes in bronchial and alveolar epithelial cell apoptosis after mechanical ventilation with different concentration oxygen inhalation and different Peak Inspiratory Pressure(PIP) and explore the mechanism and significance of cell apoptosis and MMPS in ventilator-induced lung injury of newborn rabitts, and their probable molecular mechanism as well.Methods. 108 newborn rabbits aged 1-5 days were arranged randomly to two groups by 2×3×3 factorial design according to high concentration oxygen group(FiO₂=1.0) and low concentration oxygen groups(FiO₂=0.45): Each groups were divided into three parts: high peak inspiratory pressure group (HPIP),moderate peak inspiratory pressure group (MPIP) and low peak inspiratory pressure group (LPIP). All experimental groups rabbits were done by mechanical ventilation(MV) and compared with no mechanical ventilation control group and killed to obtain lungs at 1h, 3h, 6h after trail respectively. Cells in BALF were counted and the percentage of WBC classified in sediment film. The ratio of wet to dry of lungs were detected, at the same time analyzing pathological section and the ultrastructure. MMP-2,9 expression were examined by immunohistochemistry in lung tissue pathological section and the concentration of MMP-2,9in lung tissue bomogenate were detected by ELISA, RT-PCR for the gene expression. Lung histopathology was assessed by light microscope and electron microscope. The extent and location of cell apoptosis in the bronchus and lung tissues were studied by transferase d-UTP end-labeling (TUNEL) assay and immunohistochemistry.Results: Within 6h in newborn rabbits by MV, The change of WBC classification count in BALF indicated that the cell response was different in the different ventilation way and the dissimilarity time in the same ventilation way.â‘ The white blood cells mean of ventilation with hyperxia or hypoxia groups was higher than that of control group(no MV)and with HPIP groups was higher than that of MPIP and LPIP groups (P＜0.05).The main percentage of WBC in BALF was macrophage in hypoxia or MPIP ventilation or in control group. The percentage of leukomonocyte had irrelative with oxygen concentration, but it concerned with the lung mechanical stretch and the mean was maximum under the condition of HPIP ventilation. (P＜0.05); Compared to hypoxia groups, segmented cell in hyperxia groups was high. The percentage of segmented cell of MPIP groups was significantly decreased than that of HPIP and LPIP groups(P＜0.05). The newborn rabbits lung pathological ranking and pathological score manifested that the lung injury in hyperxia groups was more Severity than that of hypoxia groups. The lung injury of MPIP ventilation groups was lightest in all of experiment groups. All experiment rabbits pathological section had alveoli pulmonum heterogeneity inflation. There were obviously part pulmonary atelectasis in LPIP groups and pulmonary hemorrhage and pulmonary bullae formation in HPIP groups. The newborn rabbits lung pathological section, pathological ranking and pathological score all manifested that the lung injury in moderate peak inspiratory pressure group was not Severity compared with low peak inspiratory pressure group and high peak inspiratory pressure group. There were obviously part pulmonary atelectasis in low peak inspiratory pressure group and pulmonary hemorrhage and pulmonary bullae formation in high peak inspiratory pressure group.â‘¡The concentration of the MMP-2 increased and the mRNA expression strengthen in different concentration oxygen groups and the expression of MMP-2 between high and low concentration oxygen groups were not significant difference, but compared with the control groups, the hyperoxia ventilation group had significant difference. The different mechanical stretch made MMP-2 expression up-regulation and the concentration of MMP-2 was not significant difference among the different PIP groups, but compared with the control groups, the MPIP ventilation groups had significant difference. There were weak correlation between MMP-2 and the ratio of wet to dry in lung and there were no correlation among MMP-2 and the total white blood cell and the percentage of WBC in BALF and the pathological lung injury score. Compared with mechanical ventilation and low concentration oxygen inhalation groups, The concentration of the MMP-9 decreased and had significant difference(F=15.660, P=0.000). The means of MMP-9 in different PIP groups and the interaction among groups were not significant difference. Compared with the control groups, the MMP-9 mRNA expression down-regulated in HPIP group and approached normal in MPIP group and LPIP group. With mechanical ventilation going, the MMP-9 mRNA expression up-regulated and near to maximum at 6h, but the ANOVA result were not significant difference. There were correlation amongMMP-9 and the total white blood cell, the percentage of macrophage in BALF, the ratio of wet to dry in lung.â‘¢There were significant different both the caspase-3 express and the ANOVA result about the Apoptotic index (AI) in different PIP groups and different concentration oxygen groups. It explain that the extent of cell apoptosis were different in MV with different PIP groups. The cell apoptosis in MPIP groups were most serious than that of HPIP and LPIP groups but the change of pathology in HPIP and LPIP groups were more serious than that of MPIP groups. With the MV going, the cell apoptosis phenomenon and lung pathologic lung were becoming more and more serious in the same PIP groups.â‘¡Compared to HPIP groups and LPIP groups, The type-â…¡cellular structure was still cube and there were less neutrophil infiltration and less cell transformation phenomenon from the type-â…¡cell to the type-â… cell in MPIP groups. However, there were more neutrophil infiltration and neutrophil apoptosis as well as there were obvious the type-â…¡cellular structure change and cell transformation phenomenon. The cell apoptosis phenomenon in high concentration oxygen groups were more serious than that of low concentration oxygen groups.Conclusions:â‘ when new-bom rabbits suffer from MV. The lung injury in hyperxia groups was more Severity than that of hypoxia groups. It is easily induced to atelectasis in the LPIP ventilation and barotrauma in the HPIP ventilation. Only MV with the MPIP can reduce the lung injury. Different cell response in BALF is determined by the different ventilation way.â‘¡Within 6h in newborn rabbits by mechanical ventilation, hyperoxia ventilation and moderate mechanical stretch can up-regulate MMP-2, but MMP-2 expression have no a significant correlation with ventilator-induced lung injury of newborn rabbits, hyperoxia ventilation can down-regulate MMP-9 expression, but different mechanical stretch have no effect on MMP-9 expression. MMP-9 expression has correlation with ventilator-induced lung injury of newborn rabbits.â‘¢Mechanical ventilation with different PIP and different concentration oxygen causes consistent changes in cell apoptosis and caspase-3 expression in newbom rabbits, but it is not consistent changes in cell apoptosis and histopathology. When mechanical stretch exert pressure to alveolar epithelial cell, appropriate stretch is important to promote epithelium apoptosis promptly and to maintain alveolus structural integrality. But impertinence or persistence stretch induce inappropriate apoptosis and make more serious lung injury. Hyperxia can aggravate lung injury. These support that cell apoptosis plays a key role in the pathogenesis of ventilator-induced lung injury.